1. Field of the Invention
The invention is generally related to aircraft oxygen breathing masks and, more particularly, to breathing masks having microphones therein.
2. Description of the Related Art
Most aircraft are equipped with breathing mask systems to supply oxygen to crew members for use in emergency situations, for instance in oxygen depleted environments during aircraft decompression. In the course of such emergency aircraft operations, pilots, navigation officers and other flight crew personnel may don a breathing mask including a demand breathing regulator and microphone system. It is imperative that the breathing mask include a microphone so that communication with other crew members or with control tower personnel, during such emergency situation may be maintained.
In most microphone systems, sounds emitted by the wearer activate a microphone which converts received sounds into audio signals for transmission. The sounds received by the microphone include not only the wearer's voice but, unfortunately, background noise as well. When the wearer inhales, the sound of gas flow through the mask's breathing regulator is often particularly loud and is transmitted as noise having a large component comparable in both frequency and intensity to the sounds made by a person when speaking. When one of two or more flight crew members wearing masks is speaking, the noise generated during inhalation by others in the crew can seriously interfere with the hearing or understanding of the crew member speaking. In addition, when the crew members are exposed to stressful emergency conditions, their breathing rate is increased further intensifying the level of noise interference. This interference presents a very serious problem because it is at such time of emergency that effective communication between crew members and the tower is imperative.
Others have endeavored to overcome the noise interference by incorporating electronic filters and noise dampening means with the microphone systems. However, it has been found that such filters and dampeners also filter out the sounds of speech.
Others have provided breathing masks wherein the microphone includes a noise attenuation structure or microphone deactivation device for reducing the amount of audio signals generated from the microphone by electrically disabling the microphone during inhalation by the wearer.
One such deactivation device has been proposed which incorporates a pair of normally closed contacts carried on a leaf spring, connected in series with the microphone and coupled with an air impingement tab disposed in the gas supply path so that incoming gas will shift such tab against the spring bias to open the contacts and disable the microphone. Such a device suffers the shortcoming that the flow of incoming air to activate the switch may lag the pilot's inhale cycle thus leaving a time lapse before the microphone is cut out when it may pick up his or her inhaling noise. Moreover, the air flow force required to overcome the bias of the contact leaf spring may be considerable and could interfere with smooth and responsive operation.
Another such deactivation device includes a normally closed electromagnetic reed switch device in circuit with the microphone. A movable magnet is disposed in the inhalation air stream of the mask to, upon movement thereof, open the reed switch to disable the microphone. Because such reed switch/magnet devices may be relatively small and require only a minimum of force to operate, such devices have been found desirable for use in breathing mask applications to minimize the bulk of the mask and minimize weight. In this deactivation device, the magnet is biased by a spring to a normal position spaced from the switch such that during exhalation when the pilot is speaking, the magnetic field of the magnet acting on the reed switch is of insufficient strength to close such switch so that the circuit for the microphone is made and voice transmission is maintained. Upon inhalation by the wearer, the air stream impinges on the magnet assembly to move the magnet against the bias of the coil spring to a position adjacent the reed switch such that the magnetic field interacts with the read switch to open the circuit disabling the microphone.
Although this reed switch/magnet configuration has proven effective in operation, certain drawbacks have been identified with regard to the spring biased magnet. In some circumstances as the coil spring is compressed or expanded, the biasing force thereof may increase as the displacement of the spring is changed. Because the volume of air stream during inhalation tapers off near the end of the inhalation cycle, the air impinging forces acting on the magnet assembly decrease. As such, the biasing force of the spring may prematurely overcome the air impinging forces and move the magnet assembly to its normal position prematurely activating the microphone before the full inhalation cycle is completed. In addition, in the case where the spring force is increased as the spring is expanded or contracted, such spring force may actually inhibit the displacement of the magnet to its operative circuit disabling position if the volume of air impinging on the magnet assembly is not sufficient. Therefore, it is desirable that the force required to move the magnet assembly decrease as the magnet assembly is moved to the circuit opening position rather than increase. Hence, those skilled in the art have recognized the need for providing a breathing mask having a microphone noise attenuation device which is effective upon inhalation by the wearer to deactivate the microphone and eliminate background and inhalation noises. Operation of the microphone noise attenuation device should be minimally affected by variations in orientations of the mask due to variations in the orientation of the wearer's head as he or she looks about in the aircraft and as the aircraft itself maneuvers about. Additionally, the noise attenuating device should incorporate a minimal number of components to facilitate rapid assembly within the breathing mask and minimize bulk. Further, the microphone attenuation device should be relatively inexpensive to manufacture and reliable in use. The present invention meets these needs and others.